Social class differences in mortality and morbidity from a wide range of diseases persist in the USA, UK and other industrialised countries. We wish to determine the extent to which psychosocial factors at work and outside account for these social class differences. The overall aim is to study: a) the effect on health and disease of the work environment - psychological workload, control over work pacing and content, opportunity for use of skills, social support at work, b) the moderating effect on these relationships of social supports, and c) the interaction between these psychosocial factors and other established risk factors in the aetiology of chronic disease. Our previous studies in the British Civil Service demonstrated a threefold higher mortality from cardiovascular and non-cardiovascular disease in the lowest compared to the highest employment grade. This difference could be explained only in part by differences in smoking, leisure-time physical activity, plasma choloesterol, blood pressure or obesity. We propose a new study, initially cross-sectional, of 11,000 civil servants, men and women aged 35-55, working in London. Assessments will be made by questionnaire and validated by interview of work characteristics, social supports, Type A behaviour pattern, stressful life circumstances. We shall quantify their relationship a) to health behaviours such as smoking, alcohol consumption and physical activity, b) to biological risk factors such as blood pressure and plasma cholesterol, c) to prevalence of cardiac and respiratory illness and d) to prevalence of neurotic disorder. We shall collect sickness absence data prospectively. In the longer term, using the sickness absence data and the National Health Service Central Death Registry, we shall examine the relationship of these psychosocial and other factors to morbidity and mortality from specific diseases. This study will take place alongside a randomised controlled trial of behaviour modification using biofeedback-aided relaxation aimed at reducing morbidity in the 1000 persons screened who are at highest risk of cardiovascular disease.